Shown in FIG. 1 is a block diagram of a conventional microwave oven having a hood including a key pad 101 for applying signals such as ventilation turn on/off signals, kind of cooking key signals, cooking period of time key signal etc., as a user intent in cooking mode, a clock generation part 102 for generating clocks in a fixed interval, a microcomputer 100 for computing the key signals received from the key pad 101 and the clocks generated in the clock generation part 102, and controlling entire system operation of the microwave oven, a ventilation relay 103 for opening/closing a ventilation opening of the ventilation motor in response to the control signals of the microcomputer 100, and a relay 104 for carrying out cooking mode by operating a magnetron and a turn table motor(not shown) in response to the control signals of the microcomputer. The microcomputer 100 has a key signal conversion part 100b for converting the key signals of the key pad 101 into corresponding data, a counter part 100a for counting the clocks in a fixed interval generated in the clock generation part 102, a controlling part 100c for distinguishing data received from the key signal conversion part 100b such as kind of cooking data, cooking period of time data and ventilation turn on/off data, and storing the kind of cooking data and the ventilation turn on/off data into a memory part 100d, computing, after storing cooking period of time data into a timer memory part 100e, the stored cooking period of time data and the counted value(actual lapse of time) of the counter part 100a and generating control signals corresponding to the computed data, a ventilation relay operation part 100f for controlling operation of a ventilation relay 103 in response to the on/off control signal generated in the control part 100c, and a relay operation part 100g for controlling operation of a relay 104 in response to the cooking period of time control signal of the control part 100c.
If cooking period of time and kind of cooking keys are selected on the key pad 101, the key signal conversion part 100b in the microcomputer 100 converts the applied cooking period of time key signal and kind of cooking key signal into corresponding data and transmits the converted data to the control part 100c.
And, the counter part 100a in the microcomputer 100 counts the clocks generated in a fixed interval in the clock generation part 102 and transmits the counted clock to the control part 100c.
The control part 100c stores kind of cooking data received from the key signal conversion part 100b into the memory part 100d, and computes total required cooking period of time referring to the stored kind of cooking data to store the computed total required cooking period of time into the timer memory part 100e.
Once the total required period of time has been computed, the control part 100c releases reset of the counter part 100a to detect actual lapse of time according to the number of clocks of the clock generation part 102 and turns on the relay 104 through the relay operation part 100g during the computed total required cooking period of time.
Upon turning-on of the relay 104, a magnetron in rear side is actuated heating food on a turn table in a heating chamber.
Thereafter, when the actual lapse of time counted in the counter part 100a matches with the total required cooking period of time stored in the timer memory part 100e, ie., when cooking has been completed, the control part 100c turns off the relay 104 through the relay operation part 100g to finish cooking operation.
Meantime, when a user presses a ventilation turn on key on a key pad 101 to discharge gas and moist from a heating chamber produced during cooking using a microwave oven, a gas range or other cookers, a key signal conversion part 100b of a microcomputer 100 converts the applied signals into corresponding data and transmits the converted data to a control part 100c.
The control part 100c stores the ventilation turn-on data of the key signal conversion part 100b into the memory part 100d and turns-on the ventilation relay 103 through the ventilation relay operation part 100f.
Upon turning on of the ventilation relay 103, a ventilation motor(not shown) in rear side is actuated to discharge gas and moisture in the heating chamber to outside.
And when a ventilation turn off key on the key pad 101 is pressed at completion of discharging gas and moisture from the heating chamber, the control part 100c of the microcomputer 100, following aforementioned process, turns off the ventilation relay 103 through the ventilation relay operation part 100f to stop the ventilation motor.
However, in the foregoing ventilation motor control system of a microwave oven having a conventional hood function, a user has to press ventilation turn on key to discharge gas and moist from a chamber through a ventilation motor, and, to finish discharge operation on completion of discharge, the user has to press ventilation turn off key again to stop operation of the ventilation motor.
Accordingly, the user has experienced inconvenience of waiting for a long time from turning on of the ventilation motor to the completion of discharge of exhaust gas to go outside, and, if the user should press the ventilation motor turn off key in advance to go outside, the ventilation operation could not be carried out any further.